To date, submersible pumps have not proved particularly satisfactory for use in stripper wells producing oil from older oil fields. As a consequence, most oil well pumps are of the walking beam type, with the power source located at the surface of the ground. One difficulty has been in devising a suitable pump of a diameter small enough to fit in small diameter casing, such as 4" casing, which is common in many older wells.
Cam driven piston devices, broadly considered, have been proposed in the past. See, for example, U.S. Pat. Nos. 165,027; 660,681; 2,291,601 and 2,508,253. A particularly effective cam follower mechanism is illustrated in U.S. Pat. No. 3,792,616.